The present invention relates to a control valve and system for a well bore and more particularly to an apparatus and method for automatically controlling the flow of fluid from a well bore. Specifically, the present invention relates to a new and improved fluid control valve mechanism for controlling or choking the fluid flow from well bores.
In the well drilling industry, it is a usual practice to provide a choke system for the drilling fluid conducted from the well bore to a receiving tank whereby the choke system maintains a predetermined level of pressure in the well bore and therefore controls the flow of fluid from that bore. The choke system is located outside of the well bore and is connected to a well casing beneath the well blowout prevention apparatus in a normal assemblage, such as shown in U.S. Pat. No. 3,552,502.
Known choke systems, such as the aforementioned patent, are employed to control the flow of fluid from a well bore after a kick or attempted blowout has occurred and work with the blowout prevention apparatus to establish and maintain proper back pressure in the well bore. The back pressure maintained by the choke system is combined with the hydrostatic pressure of the drilling fluid to prevent a back flow into the well bore during the kick. The back pressure applied by the choke system is held until hydrostatic fluid circulated into the bore has returned to the surface thus killing the well.
Known choking systems utilize a variety of choking devices, one of which is the positive choke. A positive choke has a predetermined size and is installed in a choke body and therefore must be physically changed as conditions change. Commonly changing conditions such as well bore pressure or drilled formation brought to the surface may plug the choke and necessitate its removal. The removed choke must then be either unplugged or replaced, thus resulting in costs added to the already high costs involved in well drilling operations.
Another known choke device utilizes a stationary disc with a half moon-like opening coacting with another similarly shaped movable disc. The movable disc is controlled by a shaft that transmits rotational movement thereto. When the openings of the two discs are in alignment, the choking device is in the fully open position and as the movable disc is rotated, the opening is altered to control the flow rate of fluid passing through the choke. The choke can be rotated from the above-described fully-open position into a fully-closed position wherein the half-moon opening of the movable disc assumes a position opposite to the opening of the stationary disc. However, this type of choke tends to erode very rapidly due to the manner with which flow is restricted.
Still other well choke, such as the one shown in U.S. Pat. No. 3,429,385, utilizes an open or cylindrical seat which is held stationary with respect to a plug-shaped body and uses a hydraulic cylinder to control the movement of the plug shaped body toward and away from the cylindrical seat. The distance between the seat and the plug-shaped body determines the degree to which the choke is opened with the choke being fully closed when the plug-shaped body is fully inserted into the seat. However, this choke, like the others, tends to erode rapidly and, also like the others, requires elaborate and expensive control systems and panels for satisfactory choke operation.